This invention relates to rolling element bearings and particularly to such bearings having design features for providing a more favorable sharing of loading on the bearing elements thus providing increased service life and/or load carrying capacities.
Rolling element bearings such as ball, tapered, needle, and cylindrical bearings are used in widespread applications. When rolling element bearings are used to support pure radial loads, or a combination of radial and thrust loads (as opposed to pure axial or thrust loads) they have an inner race surrounded by an outer race with rolling elements interposed between them. The operating life of rolling element bearings is related to the maximum stresses experienced by the bearing components. Cyclical application of such stresses produce fatigue damage to the bearing, leading to ultimate bearing failure. By providing a more even sharing of rolling element loading around the circumference of the races and forcing a more favorable distribution of stress at each rolling element raceway contact, bearing life and load carrying capacity can be increased. This invention is related to design features for providing such loading conditions.
In their operating environments, bearings may be exposed to applied loads which create contact stresses which are not uniform around the circumference of one of the races and act repeatedly on the same area. Consequently, the contact stress developed between the rolling elements and the bearing races vary as a function of the angular position on one or both of the races. Various design approaches are available for reducing peak contact stresses, such as enlarging the overall bearing size so that larger and more numerous rolling elements combine to restrain the applied loads. Such design approaches, however, possess tradeoffs and disadvantages of their own.
One facet of this invention involves design approaches which enable bearings to be designed in a way that peak contact stresses are reduced by causing the loading around the circumference of a bearing race to be spread out over a larger angular range. By reducing peak contact stresses, the life of the bearing can be extended, or in the alternative, the bearing can be rated to have a higher maximum external load carrying capability.
Conventional rolling element bearings have inner and outer races which are rotationally symmetrical. In other words, a radial cross-section taken at any circumferential position has the same cross-sectional shape and area. In accordance with this invention, the bearing inner and/or outer race is provided with circumferential segments which are more flexible in response to rolling element contact loads as compared with other segments. Such "structural asymmetry" can be provided by modification to the bearing mounting structure or to the bearing races themselves. In a preferred embodiment of this invention, one or both of the races have a variation in cross-sectional shape which renders certain circumferential segments less stiff than other segments. By placing the more flexible circumferential segments in the region where peak applied loads are expected, a reduction in peak contact stress occurs. This reduction provides a bearing having a longer service life characteristic and also enables the bearing to be used with higher applied loads. Various embodiments of this invention describe techniques for providing asymmetrical flexibility characteristics for the bearing.
In addition to the circumferential distribution of applied load, rolling element bearings may be subjected to misalignment between the inner and outer bearing races. Such misalignment as well as other factors can cause the force distribution along the lines of contact between the rolling elements and the races to be nonuniform. Significantly higher forces and resulting stresses can be encountered at one axial end of the rolling elements as compared to the other. In addition to conditions where one axial end of a rolling element is disproportionately loaded, transient loading conditions along the bearing element lines of contact can occur. In such conditions, the peak stress alternates between ends of the bearing elements, or one rolling element repeatedly has a higher average normal load than another element. As in the case of applied load induced stresses, a reduction in peak stress and elimination of transients along the rolling element lines of contact also tend to increase the bearing service life.
In view of the foregoing, this invention further involves techniques for producing greater uniformity in stress distribution along the bearing element contact lines by selectively providing portions of the axial length of one of the bearing races with increased flexibility. Such increased flexibility can be provided either by modification to the bearing housing or the races themselves. Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.